This invention generally relates to the operator interface of an ultrasound imaging system. In particular, the invention relates to means for input of commands for controlling the system modes of operation and for setting selectable system parameters by means of a three dimensional position sensor.
Conventional ultrasound imaging systems are capable of operating in any of a plurality of modes. The most common modes of diagnostic ultrasound imaging include B- and M-modes (used to image internal, physical structure), and the Doppler and color flow modes (the latter two being primarily used to image flow characteristics, such as in blood vessels). In conventional B-mode imaging, ultrasound scanners create images in which the brightness of a pixel is based on the intensity of the echo return. The color flow mode is typically used to detect the velocity of fluid flow toward/away from the probe, and it essentially utilizes the same technique as is used in the Doppler mode. Whereas the Doppler mode displays velocity versus time for a single selected sample volume, color flow mode displays hundreds of adjacent sample volumes simultaneously, all superimposed on a B-mode image and color-coded to represent each sample volume's velocity.
Conventional ultrasound imaging systems provide a two-dimensional image representing the biological tissue in a plane scanned by a probe. A three-dimensional volume can be imaged by moving the probe so that scanning occurs in a succession of scan planes, each scan producing a respective image frame of acquired data.
The probe is typically configured to be held in the hand of the sonographer. A typical probe comprises a transducer array seated in the distal end of a probe housing and an electrical cable penetrating the proximal end of the probe housing. The cable comprises a multiplicity of coaxial wires which connect the elements of the transducer array to the receive channels of the beamformer via a probe/system connector. A conventional transducer array comprises a multiplicity of transducer elements made of piezo-electric material. Typically, each transducer element has metallic coatings on opposing front and back faces to serve as ground and signal electrodes respectively. The signal electrodes are typically connected to respective electrical conductors formed on one or more flexible printed circuit boards (PCBs). The flexible PCBs are in turn electrically coupled to the coaxial wires of the probe cable.
By selecting the time delay (or phase) and amplitude of the voltages applied to the transducer elements, ultrasonic waves can be transmitted which combine to form a net ultrasonic wave that travels along a preferred vector direction and is focused at a selected point along the beam. The same principles apply when the transducer probe is employed to receive the reflected sound in a receive mode. The voltages produced at the receiving transducer elements are summed so that the net signal is indicative of the ultrasound reflected from a single focal point in the object. As with the transmission mode, this focused reception of the ultrasonic energy is achieved by imparting separate time delay (and/or phase shifts) and gains to the signal from each receiving transducer element. A single scan line (or small localized group of scan lines) is acquired by transmitting focused ultrasound energy at a point in the region of interest and then receiving the reflected energy over time.
In the B-mode, for example, the ultrasound image is composed of multiple image scan lines. The brightness of a pixel is based on the intensity of the echo return from the biological tissues being scanned. The outputs of the receive beamformer channels are coherently summed to form a respective pixel intensity value for each sample volume in the object region or volume of interest. These pixel intensity values are log-compressed and scan-converted to form an image frame of pixel data which can be displayed on a monitor. Multiple scans are performed in succession and multiple image frames are displayed at the acoustic frame rate on the display monitor.
In the case where the sonographer is manipulating the transducer probe by hand, one hand is used to control the position of the probe relative to the patient while the other hand is used as necessary to operate levers and keys on the control panel. For example, if the sonographer wishes to select a cut plane in an acquired three dimensional volume, the sonographer depresses a "select" button on the control panel with his free hand. There is a need for an operator interface which is reduces the operator movements required to perform ultrasound examination.
In conventional ultrasound imaging systems, manipulation of three-dimensional images is awkward and non-intuitive, particularly when trying to select cut-planes in an acquired three dimensional volume. Conventional ultrasound systems typically use some combination of one or more knobs and a track ball or mouse. At a minimum, one knob and one track ball or mouse is required to control the cut-plane's three degrees of freedom: roll, pitch, and displacement. The track ball or mouse controls the roll and pitch, while the knob controls displacement. The manipulation required is neither easy nor intuitive. As a result, there is a need for an improved method of manipulating images and other symbols displayed by ultrasound imaging systems.